CHAPTER 6

Process Selection and Facility Layout

Process selection

Forecasting

Product andService Design

TechnologicalChange

CapacityPlanning

ProcessSelection

Facilities andEquipment

Layout

WorkDesign

Process Selection and System Design.

VarietyHow much variety in products or service will the

system need to handle ? Flexibility

What degree of equipment flexibility will be needed ?

Volume What is the expected volume of output ?

Process Selection

Job shopSmall scale

BatchModerate volume

Repetitive/assembly lineHigh volumes of standardized goods or

services Continuous

Very high volumes of non-discrete goods

Process Types

Process Type

Job Shop

Appliance repair

Emergency room

Ineffective

Batch Commercial

bakingClassro

omLecture

Repetitive

Automotive

assembly

Automatic

carwash

Continuous(flow)

Ineffective Steel Production

Water purification

Product and Service Processes

Low Volume High Volume

Product – Process MatrixDimension Job shop Batch Repetitive Continuous

Job variety Very High Moderate Low Very low

Process flexibility

Very High Moderate Low Very low

Unit cost Very High Moderate Low Very low

Volume of output

Very low Low High Very High

Other issues; schedulingwork-in-process

inventorylabor skill

Important factors for process designProduct profilingSustainable goods and servicesLean process designAutomation

Facility layout

Objective of Layout Design Facilitate attainment of product quality Use workers and space efficiently Avoid bottlenecks Minimize unnecessary material handling

costs Eliminate unnecessary movement of

workers or materials Minimize production time or customer

service time Design for safety

Types of layout Fixed-Position layouts Product layouts Process layouts Cellular layouts Service layouts Combination layouts

Facilities Layout

Fixed Position Layouts Fixed Position Layout: Layout in which the

product or project remains stationary, and workers, materials, and equipment are

moved as needed. Nature of the product dictates this type of

layoutWeightSize Bulk

Large construction projects

Fixed Position Layouts (cont.) Typical of projects Equipment, workers, materials, other

resources brought to the site Highly skilled labor Often low fixed costs Typically high variable costs

Types of layout Fixed-Position layouts Product layouts Process layouts Cellular layouts Service layouts Combination layouts

Facilities Layout

Raw materialsor customer

Finished item

Station 2

Station 2

Station 3

Station 3

Station 4

Station 4

Material and/or labor

Station 1

Material and/or labor

Material and/or labor

Material and/or labor

Used for Repetitive or Continuous ProcessingProduct Layout

Product Layout (cont.)

Flow shop production -(Product orient ed layout): seeks the best personnel an

d machine utilization in repetitive or co ntinuous production.

1 2 3 4

5

6

78910

In

Out

Workers

A U-Shaped Production Line

Ease to cross-travel of workers and vehicles More compact More communication between workers

High rate of output Low unit cost Labor specialization Low material handling cost High utilization of labor and

equipment Established routing and scheduling Routine accounting, purchasing

and inventory control

Advantages of Product Layout

Creates dull, repetitive jobs Poorly skilled workers may not

maintain equipment or quality of output

Fairly inflexible to changes in volume Highly susceptible to shutdowns Needs preventive maintenance Individual incentive plans are

impractical

Disadvantages of Product Layout

Types of layout Fixed-Position layouts Product layouts Process layouts Cellular layouts Service layouts Combination layouts

Facilities Layout

Dept. A

Dept. B Dept. D

Dept. C

Dept. F

Dept. E

Used for Intermittent processingJob Shop or Batch Processes

Process Layout(functional)

Process Layout

Can handle a variety of processing requirements

Not particularly vulnerable to equipment failures

Equipment used is less costly Possible to use individual incentive

plans

Advantages of Process Layouts

In-process inventory costs can be high Challenging routing and scheduling Equipment utilization rates are low Material handling slow and inefficient Complexities often reduce span of

supervision Special attention for each product or

customer Accounting and purchasing are more

complicated

Disadvantages of Process Layouts

- Process oriented layout Design places departments with

large flows of material or people together

Department areas having similar processes located in close proximity

- Process oriented layout(cont.) Steps in Developing a Process-

Oriented Layout1. Construct a “from-to matrix”station

station

- Process oriented layout(cont.) Steps in Developing a Process-

Oriented Layout2.Determine space requirements for each department

- Process oriented layout(cont.) Steps in Developing a Process-

Oriented Layout3. Develop an initial schematic diagram

- Process oriented layout(cont.) Steps in Developing a Process-Oriented Layout

Cost of Process-Oriented Layout

Minimize cost = ∑∑ XijCij

Where n = total number of work centers or departments

i,j = individual departmentsXij = number of loads moved from department i

to department jCij = cost to move a load between department

i and department j

n n

i=1j=1

- Process oriented layout(cont.) Steps in Developing a Process-

Oriented Layout4. Determine the cost of the layout

Cost of moving 1 unit between adjacent departments is 1 dollar

Cost of moving 1 unit between nonadjacent departments is 2 dollar

- Process oriented layout(cont.) Possible Layout 2

- Process oriented layout(cont.) Interdepartmental Flow Graph

Showing Number of Weekly Loads

Types of layout Fixed-Position layouts Product layouts Process layouts Cellular layouts Service layouts Combination layouts

Facilities Layout

Benefits:Minimal work in processReduced space requirementsReduced lead timeProductivity and quality improvementIncreased flexibility

Cellular Layouts

Cellular manufacturing systems (w ork cell layout): arranges machinery a

nd equipment to focus on production o f a single product or group of related p

roducts

Cellular Layouts (cont.)• Work Cells

Cellular Layouts (cont.)• Work Cells

Advantages and Disadvantages of Cellular Layouts Advantages

Minimal work in process

Reduced space requirements

Reduced lead time

Productivity and quality improvement

Increased flexibility

Disadvantages

Expanded training and scheduling of workers

Increased capital investment

Types of layout Fixed-Position layouts Product layouts Process layouts Cellular layouts Service layouts Combination layouts

Facilities Layout

Office layouts Retail layouts Warehouse and storage layouts

Service Layouts

Service Layouts (cont.) Office Layouts

Office layouts

Service Layouts (cont.) Retail layouts

Design maximizes product exposure to customers

Decision variableStore flow patternAllocation of (shelf) space to products

Service Layouts (cont.) Warehouse and storage layouts

Types of layout Fixed-Position layouts Product layouts Process layouts Cellular layouts Service layouts Combination layouts

Facilities Layout

Line balancing

Line Balancing is the process of assigning tasks to workstations in such a way that the workstations have approximately equal time requirements.

Design Product Layouts: Line Balancing

Assign tasks in order of most following tasks.

Count the number of tasks that followAssign tasks in order of greatest positional weight.

Positional weight is the sum of each task’s time and the times of all following tasks.

Some Heuristic (intuitive) Rules:Line Balancing Rules

Line Balancing Rules (cont.)

Cycle time is the maximum time allowed at each workstation tocomplete its set of tasks on a unit.

Cycle Time

Determine Maximum OutputOutput rate = OT

CT

CT = cycle time = OT D

Where OT = Operating time per day D = Desired output rate

task timeof sum = t

CT

t)( =N

Determine the Minimum Number of Workstations Required

N = Minimum number of work station

Where

Precedence diagram: Tool used in line balancing to display elemental tasks and sequence requirements

A Simple Precedence

Diagram

a b

c d e

0.1 min.

0.7 min.

1.0 min.

0.5 min.

0.2 min.

Precedence Diagram

Percent idle time = Idle time per cycle

(N)(CT)

Efficiency = 100 – Percent idle time

Calculate Percent Idle Time

Example 1 Plan to produce 400 units in 1 day (8 hours)

Immediate Task time Task follower (min) a b 0.2 b e 0.2 c d 0.8 d f 0.6 e f 0.3 f g 1.0 g h 0.4 h end 0.3

Solution to Example 1 (cont.)

c d

a b e

f g h

0.2 0.2 0.3

0.8 0.6

1.0 0.4 0.3

Solution to Example 1 (cont.)

CT = cycle time = 480 =1.2 min

N = 3.8 = 4

400

1.2

Station 1 Station 2 Station 3 Station 4

a b ef

d

g h

c

Solution to Example 1 (cont.)

Solution to Example 1 (cont.)

Percent idle time = Idle time per cycle (N) (CT) = 1 . 4x1.2 = 20.8%

Efficiency = 100 – Percent idle time = 100- 20.8 = 72.9 %

Solution to Example 1 (cont.)

Move b from station 1 to station 2

Solution to Example 1 (cont.)

Percent idle time = Idle time per cycle (N) (CT) = 0.6 . 4x1.1 = 13.6%

Efficiency = 100 – Percent idle time = 100- 13.6 = 86.4 %

1 min.2 min.1 min.1 min.30/hr. 30/hr. 30/hr. 30/hr.

Bottleneck

Bottleneck Workstation

Parallel Workstations

1 min.

2 min.

1 min.1 min.60/hr.30/hr. 30/hr.

60/hr.

2 min.30/hr.

30/hr.Parallel Workstations

Example TN5.2Assembly-Line BalancingThe Model J Wagon is to be assembled on a conveyor belt. 500 wagons are required per day.Production time per day is 420 minutes, and the assembly steps and times for the wagon are give inExhibit TN5.10 Assignment: Find the balance that minimizes the number of workstations, subject toCycle time and precedence constraints.

SOLUTION1. Draw a precedence diagram. Exhibit TN5.11 Illustrates the sequential relationships identified

in Exhibit TN5.10(The length of the arrows has no meaning.)

Example TN5.2 (cont.)

Example TN5.2 (cont.)

Example TN5.2 (cont.)

Example TN5.2 (cont.)

Ex 03Firm determines that there are 480 productive minutes are available per day.The production schedule requirement is 40 units be completed as output fromthe assembly line each day. Determine cycle time, number of work stations,

efficiency.

Ex 03 (cont.)

Ex 03 (cont.)

CT = cycle time = Production time available per day Units required per day

= 480

= 12 min N = 66

= 5.5 or 6 stations

40

12

Ex 03 (cont.)

Ex 03 (cont.)

Efficiency = Task time . (actual number of workstations) x (largest cycle time)

= 66 minutes . ( 6 stations) x (12 minutes)

= 91.7 %

Ex 04The Toy company has decided to manufacture a new toy, the production ofWhich is broken into six steps. The demand for toy is 4800 units per 40 hour-week

a) Draw a precedence diagram of this operationb) Given the demand, what is the cycle time of operation ?c) What is theoretical minimum number of workstations ?d) Assign tasks to workstations ?e) What is efficiency of the assembly line if number of station 4, 5 or 6 ?

Ex 04

Ex 04

Ex 04

Comparison of Product and Process Layouts

Description

Type of process

Product

Demand Volume Equipment

Description

Type of process

Product

Demand Volume Equipment

Sequential arrangement of activities

Continuous, mass production, mainly assembly

Standardized, made to stock

Stable High Special purpose

Process Functional

grouping of activities

Intermittent, job shop, batch production, mainly fabrication

Varied, made to order

Fluctuating Low General purpose

Product

Comparison of Product and Process Layouts (cont.)

Workers Inventory

Storage space Material handling Aisles Scheduling Layout decision Goal

Advantage

Workers Inventory

Storage space Material handling Aisles Scheduling Layout decision Goal

Advantage

Limited skills Low in-process, high

finished goods Small Fixed path (conveyor) Narrow Part of balancing /Line Line balancing Equalize work at each

station Efficiency

Process Varied skills High in-process, low

finished goods Large Variable path (forklift) Wide Dynamic / Orders Machine location Minimize material

handling cost Flexibility

Product

Quiz 1

Cycle = 1 minutes

จงทำ��ให้ Line Balance โดยแนวคิ�ดของ Ranked positional weight

Quiz 1

Quiz 1 ห้�คิ�� Ranging ของแต่�ละง�นออกม�ก�อน (ห้�เวล�ของง�นทำ��งห้มดทำ��ต่�มห้ล�งม� + เวล�ของต่�วม�น

เอง) Station 12 ม�เวล�ของง�นรวมทำ��งห้มด 0.12 Station 11 ม�เวล�ของง�นรวมทำ��งห้มด 0.5 + 0.12 = 0.62 Station 10 ม�เวล�ของง�นรวมทำ��งห้มด 0.62 + 0.38 = 1 Station 9 ม�เวล�ของง�นรวมทำ��งห้มด 0.27 + 0.5 + 0.12 = 0.89 Station 8 ม�เวล�ของง�นรวมทำ��งห้มด 0.6 + 0.27 + 0.38 + 0.5 + 0.12 = 1.87 Station 7 ม�เวล�ของง�นรวมทำ��งห้มด 0.32 + 0.27 + 0.5 + 0.12 = 1.21 Station 6 ม�เวล�ของง�นรวมทำ��งห้มด 0.11 + 0.27 + 0.5 + 0.12 = 1 Station 5 ม�เวล�ของง�นรวมทำ��งห้มด 0.3 + 0.38 + 0.5 + 0.12 = 1.3 Station 4 ม�เวล�ของง�นรวมทำ��งห้มด 0.1 + 0.6 + 0.38 + 0.27 + 0.5 + 0.12 = 1.97 Station 3 ม�เวล�ของง�นรวมทำ��งห้มด 0.7 + 0.11 + 0.32 + 0.6 +0.27 + 0.38 + 0.5

+0.12 = 3 Station 2 ม�เวล�ของง�นรวมทำ��งห้มด 0.4 + 0.1 + 0.3 + 0.6 + 0.38 +0.27 + 0.5 + 0.12

= 2.67 Station 1 ม�เวล�ของง�นรวมทำ��งห้มด 0.2 + 0.7 + 0.1 +0.11 + 0.32 + 0.6 + 0.38

+0.27 + 0.5 + 0.12 = 3.3

Quiz 1

Homeworkก��ห้นดให้ cycle Time = 1 น�ทำ� จงทำ��ให้ Line Balance โดยแนวคิ�ดของ Longest

task time method (ให้เล!อกง�นทำ��ต่องใช้เวล�ม�กม�ทำ��ก�อน)

Homework (cont.)

Homework (cont.)